1. Field of the Invention
This invention relates to an electron emission apparatus comprising electron-emitting devices, an image-forming apparatus and a voltage application apparatus for applying a voltage between electrodes.
2. Related Background Art
Known electron emission apparatus include image-forming apparatus such as an electron-beam display panel realized by arranging in parallel an electron source substrate carrying thereon a large number of cold cathode electron-emitting devices, a metal back or transparent electrode for accelerating electrons emitted from the electron-emitting devices and an anode substrate provided with a fluorescent body and evacuating the inside. An image-forming apparatus comprising field emission type electron-emitting devices is described in I. Brodie, xe2x80x9cAdvanced technology: flat cold-cathode CRT""sxe2x80x9d, Information Display, 1/89, 17 (1989). An image-forming apparatus comprising surface conduction electron-emitting devices is disclosed in U.S. Pat. No. 5,066,883. A plane type electron-beam display panel can be made lightweight and have a large display screen as compared with currently popular cathode ray tubes (CRTs) and can provide brighter and higher quality images than any other plane type display panels such as plane type display panels using liquid crystals, plasma displays and electroluminescent displays.
FIG. 17 of the accompanying drawings schematically illustrates an electron-beam display panel as an example of an image-forming apparatus comprising electron-emitting devices. Referring to FIG. 17, there is shown a vacuum envelope 48 comprising a rear plate 31 operating as electron source substrate, a face plate 47 operating as anode substrate, an outer frame 42, a glass substrate 41 supporting the rear plate. The vacuum envelope 48 contains therein electron-emitting devices 34, wiring electrodes 32 (scan electrodes) and 33 (signal electrodes) connected to the respective device electrodes. Otherwise, there is shown a glass substrate 46 of the face plate 47, a transparent electrode (anode) 44 and a fluorescent body (fluorescent film) 45. The scan electrodes 32 and the signal electrodes 33 are arranged rectangularly relative to each other to produce a wiring matrix.
The display panel displays an image when selected ones of the electron-emitting devices 34 located at the crossings of the matrix are driven to emit electrons by sequentially applying a given voltage to the scan electrodes 32 and the signal electrodes 33 and the fluorescent body 45 is irradiated with emitted electrons to produce bright spots at locations corresponding to the activated respective electron-emitting devices. A High voltage Hv is applied to the transparent electrode 44 in order to give it a high electric potential relative to the electron-emitting devices 34 and accelerate the emitted electrons so that the bright spots may emit light actively. The voltage applied to the transparent electrode 44 is between several hundred volts to several tens of kilovolts depending on the performance of the fluorescent body. Therefore, the rear plate 31 and the face plate 46 are separated from each other normally by a distance between a hundred micrometers and several millimeters in order to prevent dielectric breakdown of a vacuum (electric discharges) from occurring due to the applied voltage.
While a transparent electrode is used as an acceleration electrode in the above arrangement, alternatively the fluorescent body 45 may be formed directly on the glass substrate 46 and a metal back may be arranged thereon so that a high voltage may be applied to the latter in order to accelerate electrons.
FIGS. 18A and 18B of the accompanying drawings schematically illustrate two possible arrangements of fluorescent film that can be used for an electron-beam display panel. While the fluorescent film comprises only a single fluorescent body if the display panel is used for showing black and white pictures, it needs to comprise for displaying color pictures black conductive members 91 and fluorescent bodies 92, of which the former are referred to as black stripes (FIG. 18A) or a black matrix (FIG. 18B) depending on the arrangement of the fluorescent bodies. Black stripes or a black matrix are arranged for a color display panel in order to make mixing of the fluorescent bodies 92 of the three different primary colors less discriminable and weaken the adverse effect of reducing the contrast of displayed images of reflected external light by blackening the surrounding areas. While graphite is normally used as a principal ingredient of the black stripes, other conductive material having low light transmissivity and reflectivity may alternatively be used.
A precipitation or printing technique can be suitably used for applying a fluorescent material on the glass substrate regardless of black and white or color display. The metal back is provided in order to enhance the luminance of the display panel by causing the rays of light emitted from the fluorescent bodies and directed to the inside of the envelope to be mirror-reflected toward the face plate 47, to use it as an electrode for applying an accelerating voltage to electron beams and to protect the fluorescent bodies against damages that may be caused when negative ions generated inside the envelope collide with them. It is prepared by smoothing the inner surface of the fluorescent film (in an operation normally called xe2x80x9cfilmingxe2x80x9d) and depositing an Al film thereon after forming the fluorescent film.
A transparent electrode (not shown) may be formed on the face plate 47 facing the outer surface of the fluorescent film 45 (the side facing the glass substrate 46) in order to raise the conductiveness of the fluorescent film 45.
Care should be taken to accurately align each of color fluorescent bodies and the corresponding electron-emitting device for a color display.
When a plane type image-forming apparatus using electron beams is made to have a large display screen, structural members called spacers may be required to protect the envelope against the pressure difference between the internal vacuum and the external atmospheric pressure. When spacers are used, they can become electrically charged as some electrons emitted from the electron source at locations near the spacers and/or cations ionized by electrons collide with the spacers directly or after being reflected by the face plate. When the spacers are strongly charged, electrons emitted from the electron source can be deflected to show respective swerved trajectories and get to the target fluorescent bodies at improper spots to display a distorted image having an uneven brightness distribution.
Techniques for solving the problem of electrically charged spacers by causing a small electric current to flow through the spacers have been proposed (see, inter alia, Japanese Patent Applications Laid-Open Nos. 57-118355 and 61-124031). According to one of such techniques, an electrically highly resistive film is formed-on the surface of each insulating spacer to make a slight electric current flow therethrough.
Meanwhile, in an image-forming apparatus of the type under consideration comprising an oppositely disposed positive electrode such as a metal back or a transparent electrode, a high voltage is advantageously applied thereto in order to accelerate electrons emitted from cold cathode electron-emitting devices of the electron source so that the fluorescent bodies are made to emit light to a maximum extent. Additionally, the distance separating the opposite electrode from the electron source should be minimized to display images with an enhanced degree of resolution because otherwise the electron beams emitted from the electron source can be dispersed before they get to the target electrode depending on the type of the electron-emitting devices of the electron source.
Then, a strong electric field is produced between the opposite electrode and the electron source due to the high voltage to give rise to electric discharges that can destruct some of the electron-emitting devices 34 and/or electric currents that can intensively flow through part of the fluorescent bodies to make the display screen partly and irregularly emit light.
Thus, measures should be taken to reduce the frequency of electric discharges and/or prevent electric discharge destructions from taking place.
An electric discharge destruction can occur when a large electric current flows through certain spots of the electron source generates heat that destroys the electron-emitting devices located there or instantaneously raises the voltage being applied to some of the electron-emitting devices to consequently destroys them.
Measures that can be taken to reduce the electric current leading to an electric discharge destruction may include the use of a limitter-resistor inserted in series as shown in FIG. 19. However, such a measure by turn gives rise to another problem when a large number of electron-emitting devices are arranged in rows and columns, for example in 500 rows and 1,000 columns, and connected to a matrix wiring system so that they are driven sequentially on a line by line basis in such a way that as many as 1,000 devices are activated simultaneously. Assume now that about 1,000 devices are activated and each of them generates an emission current of 5 xcexcA. Then, the electric current flowing through the anodes fluctuates between 0 and 5 xcexcA depending on the image being displayed. Thus, when a resistor of 1 Mxcexa9 is connected externally in series as shown in FIG. 19, a voltage drop of 0 to 5 kV can take place to give rise to an irregularity of as much as 50% in the brightness for the acceleration voltage of 10 kV.
Additionally, since a high voltage is applied between a pair of oppositely disposed plates, the electric charge that can be accumulated due to the capacitor effect of the display apparatus will be as much as 10xe2x88x926 coulombs if the cathode and the anode have a surface area of 100 cm2 and are separated by a distance of 1 mm and the potential difference between them is equal to 10 kV. This means that an electric discharge of 1 xcexcsec. will cause an electric current of 1 A to flow through a single spot in the display apparatus, which is sufficiently strong to destroy the electron-emitting devices. Thus, the arrangement of an external resistor that is connected in series does not provide any satisfactory solution unless it can solve the problem of uneven brightness.
Therefore, the object of the present invention is to provide an improvement to the arrangement of voltage application for an image-forming apparatus of the type under consideration.
According to a first aspect of the invention, there is provided an electron emission apparatus comprising a substrate carrying thereon electron-emitting devices, an electrode disposed opposite to said substrate and an acceleration voltage-applying means for supplying a voltage to accelerate electrons emitted from said electron-emitting devices, characterized in that said electrode is divided into a plurality of electrode segments, each being connected to said accelerating voltage-applying means by way of a resistor, and a constant voltage is applied to each and all of said electrode segments.
According to a second aspect of the invention, there is provided an electron emission apparatus comprising a substrate carrying thereon electron-emitting devices, an electrode disposed opposite to said substrate and a power source for supplying a voltage to accelerate electrons emitted from said electron-emitting devices, characterized in that said electrode is divided into a plurality electrode segments, each being connected to said accelerating voltage-applying means by way of a resistor, and a constant voltage is applied to each and all of said electrode segments.
For the purpose of the invention, a constant voltage refers to a voltage that is not subjected to switching between a value representing a clear and substantive operating state and another distinct value or between ON and OFF.
In an electron emission apparatus according to the first or second aspect of the invention, said electrode is arranged on a second substrate disposed opposite to said substrate carrying thereon said electron-emitting devices, or the first substrate and said electron emission apparatus additionally comprises a supporting member for securing a predetermined gap between said first and second substrates. Said support member operates to suppress any variations in the gap between the first and second substrates due to the difference between the pressure between the first and second substrates and the external pressure and maintain the gap between said first and second substrate substantially to a same level.
Said supporting member may be adapted to flow an electric current between said first and second substrates.
Said supporting member may be electroconductive and electrically connected to one or less than one of said electrode segments. That is to say, the supporting member is electrically connected to only one electrode segment or not electrically connected to any of the electrode segments. If such is the case, the supporting member may comprise a first member having a first electroconductivity and a second member having a second electroconductivity and electrically connecting said one or less than one of said electrode segments and said first member.
When the supporting member is electroconductive and connected to two or more than two of the electrode segments, the latter also become electrically connected by way of the former. Therefore, if the supporting member is electroconductive, it should not be connected to any of the electrode segments or should be connected only to one of the electrode segments. If the supporting member is adapted to flow an electric current between the first and second substrates, preferably it is electrically connected only to one of the electrode segments so that the electrode segment may operate as means for flowing an electric current to the supporting member or at least as part of such means to simplify the entire configuration. When, the supporting member is electroconductive, the problem of electric charge can be alleviated on the part of the supporting member if it becomes electrically charged. The degree of electroconductivity of the supporting member should be selected in view of the fact that a reduced electric charge of the supporting member is an offset to its power consumption because the use of a highly electroconductive supporting member results in a high power consumption rate. When the electroconductive supporting member is electrically connected to the electrode, a second member that is more electroconductive than the supporting member may be arranged at the site of connection.
While a rather low level of electroconductivity is selected for the supporting member to reduce its electric charge, taking its power consumption rate into consideration, the supporting member may be made to comprise a second member having a second electroconductivity higher than the electroconductivity of the first member in order to improve the electric connection with the electrode. Then, there arises a problem that the electrode segments can become short-circuited by way of the second electroconductive member. This problem can be solved by arranging the supporting member so as not to bridge a plurality of electrode segments.
In an electron emission apparatus according to the invention and comprising a supporting member disposed between the first and second substrates, the supporting member may be arranged to bridge two or more than two of the electrode segments and include a first member having a first electroconductivity and two or more than two second members having a second electroconductivity, said two or more than two second members being electrically connected respectively to said two or more than two electrode segments, said two or more than two second members being separated from each other, said second electroconductivity being higher than said first electroconductivity.
When the supporting member comprises a first member having a first electroconductivity and a second member having a second electroconductivity arranged at the site of electric connection of the supporting member and the electrode to improve the electric connection and bridges at least two of the electrode segments of the electrode, the electrode segments can become easily short-circuited by the electrically highly conductive second member. This problem can be dissolved by using two or more than two second members having the high second electroconductivity that are separated from each other and electrically connected to the two or more than two electrode segments respectively. Then, the first electroconductivity of the first member may be selected such that the short-circuiting among the plurality of electrode segments can be effectively suppressed below a permissible level. While the first electroconductivity may be selected to be low from the viewpoint of suppressing the power consumption rate of the supporting member, the effect of suppressing the short-circuiting and that of reducing the possible electric charge may also have to be taken into consideration.
When a supporting member is disposed between the first and second substrates of an electron emission apparatus according to the invention, it may be so arranged that the supporting member bridges two or more than two of the electrode segments and includes a first member having a first electroconductivity and a second member having a second electroconductivity, said second member being electrically connected to some of said two or more than two of the electrode segments, said second member being insulated from the rest of said two or more than two electrode segments, said second electroconductivity being higher than said first electroconductivity.
When the supporting member includes a first member having a first electroconductivity and electrically connected to said electrode and a second member having a second electroconductivity arranged at the site of electric connection of the supporting member and the electrode to improve the electric connection and bridges at least two of the electrode segments of the electrode, the electrode segments can become easily short-circuited by the electrically highly conductive second member. This problem can be dissolved by electrically connecting the supporting member to some of the electrode segments at positions abutting the latter whereas it is electrically insulated from the rest of the electrode segments. With this arrangement, the number of electrode segments short-circuited by the second member can be reduced. Preferably, the supporting member is electrically connected to only one of the electrode segments at a position where they but each other. More specifically, this arrangement can be realized by using an electrically conductive adhesive agent for the electric connection and a dielectric adhesive agent for the electric insulation. With this arrangement, the first electroconductivity may be such that the short-circuiting among the plurality of electrode segments can be effectively suppressed below a permissible level. While the first electroconductivity may be selected to be low from the viewpoint of suppressing the power consumption rate of the supporting member, the effect of suppressing the short-circuiting and that of reducing the possible electric charge may also have to be taken into consideration.
When the supporting member of an electron emission apparatus according to the invention includes a first member having a first electroconductivity and a second member having a second electroconductivity, preferably the surface resistance of the second member having the second electroconductivity is between 10xe2x88x921 and 10xe2x88x922 xcexa9 and that of the first member having the first electroconductivity is between 108 and 1011 xcexa9.
The electroconductive supporting member of an electron emission apparatus according to the invention may be prepared in various different ways. As a specific example, it may be prepared by forming an electroconductive film on the surface of its substrate. Then, a desired level of electroconductivity can be realized for the supporting member by appropriately selecting the material, the composition, the thickness and the profile of the film.
For the purpose of the invention, the voltage to be applied to each of the electrode segments may be selected appropriately.
According to another aspect of the invention, there is provided an electron emission apparatus comprising a first substrate carrying thereon electron-emitting devices, a second substrate carrying an electrode and disposed opposite to the first substrate, a support member for securing a predetermined gap between said first and second substrates and an acceleration voltage-applying means for supplying a voltage to accelerate electrons emitted from said electron-emitting devices, characterized in that said electrode is divided into a plurality of electrode segments, each being connected to said accelerating voltage-applying means by way of a resistor, and said supporting member is electroconductive and electrically connected to one or less than one of said electrode segments.
According to still another aspect of the invention, there is provided an electron emission apparatus comprising a first substrate carrying thereon electron-emitting devices, a second substrate carrying an electrode and disposed opposite to the first substrate, a support member for securing a predetermined gap between said first and second substrates and a power source for supplying a voltage to accelerate electrons emitted from said electron-emitting devices, characterized in that said electrode is divided into a plurality of electrode segments, each being connected to said power source by way of a resistor, and said supporting member is electroconductive and electrically connected to one or less than one of said electrode segments.
According to a further aspect of the invention, there is provided an electron emission apparatus comprising a first substrate carrying thereon electron-emitting devices, a second substrate carrying an electrode and disposed opposite to the first substrate, a support member for securing a predetermined gap between said first and second substrates and an acceleration voltage-applying means for supplying a voltage to accelerate electrons emitted from said electron-emitting devices, characterized in that said electrode is divided into a plurality of electrode segments, each being connected to said accelerating voltage-applying means by way of a resistor, and said supporting member bridges two or more than two of said electrode segments and includes a first member having a first electroconductivity and two or more than two second members having a second electroconductivity, said two or more than two second members being electrically connected respectively to said two or more than two electrode segments, said two or more than two second members being separated from each other, said second electroconductivity being higher than said first electroconductivity.
According to a further aspect of the invention, there is provided an electron emission apparatus comprising a first substrate carrying thereon electron-emitting devices, a second substrate carrying an electrode and disposed opposite to the first substrate, a support member for securing a predetermined gap between said first and second substrates and a power source for supplying a voltage to accelerate electrons emitted from said electron-emitting devices, characterized in that said electrode is divided into a plurality of electrode segments, each being connected to said power source by way of a resistor, and said supporting member bridges two or more than two of the electrode segments and includes a first member having a first electroconductivity and a second member having a second electroconductivity, and said second member being electrically connected to some of said two or more than two of the electrode segments, said second member being insulated from the rest of said two or more than two electrode segments, said second electroconductivity being higher than said first electroconductivity.
According to a still further aspect of the invention, there is provided an electron emission apparatus comprising a substrate carrying thereon electron-emitting devices, an electrode disposed opposite to said substrate and an acceleration voltage-applying means for supplying a voltage to accelerate electrons emitted from said electron-emitting devices, characterized in that said electrode is divided into a plurality of electrode segments, each being connected to said accelerating voltage-applying means by way of a resistor, and a selected voltage is applied to each of said electrode segments.
According to a still further aspect of the invention, there is provided an electron emission apparatus comprising a substrate carrying thereon electron-emitting devices, an electrode disposed opposite to said substrate and a power source for supplying a voltage to accelerate electrons emitted from electron-emitting devices, characterized in that said electrode is divided into a plurality of electrode segments, each being connected to said accelerating voltage-applying means by way of a resistor, and a selected voltage is applied to each of said electrode segments. For the purpose of the invention, the electrode segments may be connected to respective voltage-applying means or power sources in order to apply selected voltages to the electrode segments respectively.
For the purpose of the invention, the electrode segments and the respective resistors may be connected in various different ways. For example, the electrode segments and the resistors may be arranged on a plane and electrically connected on that plane. Alternatively, the electrode segments may be arranged on the respective resistors as shown in FIG. 21. More specifically, a base electrode is arranged on the substrate for carrying electrode segments and electrically connected to the voltage-applying means or the power source and resistors are arranged thereon before the electrode segments are arranged further thereon. With this arrangement, the electrode segments are connected to the voltage-applying means or the power source by way of the respective resistors and the base electrode. With any arrangement, the electrode segments are connected to the power source by way of the respective resistors and arranged in parallel with each other.
For the purpose of the invention, a plurality of electron-emitting devices are arranged and the fluctuations in the electric current flowing into each of the electrode segments and hence the fluctuations in the voltage drop due to the fluctuations in the electric current can be minimized by arranging the plurality of electron-emitting devices, which may be driven simultaneously, in a direction not parallel with the direction along which the electrode is divided into the electrode segments.
For the purpose of the invention, the resistors have a resistance between 10 kxcexa9 and 1 Gxcexa9, preferably between 10 kxcexa9 and 4 Mxcexa9.
For the purpose of the invention, a plurality of electron-emitting devices are arranged and, if the resistors have a resistance of R, each of the electron-emitting devices shows an emission current of Ie, the electrode applies an acceleration voltage of V and the number of electron-emitting devices emitting one of the electrode segments is n, preferably the relationship as defined below is met.
Rxe2x89xa60.004xc3x97V/(nxc3x97Ie)
For the purpose of the invention, the electron-emitting devices are preferably surface conduction electron-emitting devices.
According to a still further aspect of the invention, there is provided an image-forming apparatus comprising an electron emission apparatus according to the invention and an image-forming member, characterized in that images are produced on the image-forming member by electrons emitted from the electron-emitting devices.
For the purpose of the invention, the image-forming member may be an electron emitting body or a fluorescent body that emits light when irradiated with electrons.
Said image-forming member may be arranged on the substrate on which the electrode segments are disposed.
Said electrode segments may include at least one electrode showing a horizontal to vertical dimensional ratio of 4:3 or the assembled electrode segments may show a horizontal to vertical dimensional ratio of 16:9.
According to the invention, there is also provided a voltage application apparatus comprising opposite disposed first and second electrodes and a voltage-applying means for providing said first electrode with a relatively low electric potential and said second electrode with a relatively high electric potential, characterized in that said second electrode is divided into electrode segments and a constant voltage is applied to each and all of the electrode segments.
According to the invention, there is also provided a voltage application apparatus comprising opposite disposed first and second electrodes and a power source for providing said first electrode with a relatively low electric potential and said second electrode with a relatively high electric potential, characterized in that said second electrode is divided into electrode segments and a constant voltage is applied to each and all of the electrode segments.
According to the invention, there is also provided a voltage application apparatus comprising opposite disposed first and second electrodes and a voltage-applying means for providing said first electrode with a relatively low electric potential and said second electrode with a relatively high electric potential, characterized in that said second electrode is divided into electrode segments and a selected voltage is applied to each of the electrode segments.
According to the invention, there is also provided a voltage application apparatus comprising opposite disposed first and second electrodes and a power source for providing said first electrode with a relatively low electric potential and said second electrode with a relatively high electric potential, characterized in that said second electrode is divided into electrode segments and a selected voltage is applied to each of the electrode segments.